text: “[M]ass is the amount of &quot;matter&quot; in an object (though &quot;matter&quot; may be difficult to define), whereas weight is the force exerted on an object by gravity.” (Wikipedia quoting [de Silva, G.M.S. (2002), Basic Metrology for ISO 9000 Certification, Butterworth-Heinemann, 214p.]
  Well-known relationship:
  $$
  W = m \times g
  $$
  where W is weight, m is mass and g is the acceleration of gravity.
  Because g is a constant that cancels out in a ratio, mass/mass and weight/weight are identical.
  Likewise, the ratios % m/m and % W/W are identical.